Liquefying and storing a gas

ABSTRACT

Apparatus and methods for improving the safety and efficiency and decreasing the cost of producing liquid oxygen with a small-scale use liquefaction device, according to various embodiments of the present invention. In one embodiment, a switch is electrically coupled to a storage dewar pressurizing means, the switch positioned to be activated by a portable dewar upon engagement of portable dewar with storage dewar. Cryocooler and/or cooling fan enter low power mode when dewar liquid level reaches a predetermined level, and to return to a fall power mode when dewar liquid level drops to another predetermined level. A cold finger of the cryocooler extends within the dewar and may prevent overfilling of the dewar. The cold finger has a temperature gradient. As the gas liquefies and fills the dewar, the liquid level rises only to a level on the cold finger at which the temperature exceeds the boiling point of oxygen.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication No. 60/622,483, entitled “Liquefying and Storing a Gas” andfiled on Oct. 26, 2004. The present application also claims the benefitof U.S. Provisional Patent Application No. 60/677,661, entitled“Liquefying and Storing a Gas” and filed on May 2, 2005. Theaforementioned applications are hereby incorporated by reference hereinin their entirety for all purposes.

The present application is further related to U.S. patent applicationSer. No. 11/131,071 entitled “Liquefying and Storing a Gas,” filed on adate even herewith and assigned to an entity common hereto, the contentsof which are herein incorporated by reference in their entirety for allpurposes.

COPYRIGHT NOTICE

Contained herein is material that is subject to copyright protection.The copyright owner has no objection to the facsimile reproduction ofthe patent disclosure by any person as it appears in the Patent andTrademark Office patent files or records, but otherwise reserves allrights to the copyright whatsoever. Copyright© In-X Corporation 2004,2005.

FIELD

The present application relates to the production and storage ofliquefied gases at the site where at least some of the liquefied gas isto be used. In particular, the present invention relates to theproduction and storage of liquid oxygen in an oxygen patient'sresidence, and the improvement of cost, safety, and/or efficiencythereof.

BACKGROUND

The liquefaction of low boiling point gases, such as air and thecomponents of air, such as oxygen, nitrogen and argon, has beenpracticed for over 100 years, and the liquefaction of such gases on anindustrial scale has been practiced since the beginning of the 20thcentury. Typically, commercial liquefiers are designed to producehundreds of tons of liquid cryogens per day. Such industrial liquefiersare reliable, and are capable of producing liquefied gas with relativelyhigh energy efficiency. For consumers of liquefied gas requiringrelatively small quantities, small insulated containers, known asdewars, are filled with liquefied gas produced by commercial facilitiesand transported to the consumer. Consumers of small quantities ofliquefied gas include hospitals, which require oxygen for delivery topatients and nitrogen for use as a refrigerant. Also, people sufferingfrom chronic respiratory insufficiency that have been prescribed homeoxygen by their physicians may have liquefied oxygen delivered to theirresidences.

Initially, attempts to provide such a liquefier involved efforts tominiaturize large scale liquefying plants. However, due to thecomplexity of such systems, which are typically based on the Claudecycle or its variants, these attempts failed. Also, the extremely smallmechanical components resulting from the miniaturization of suchliquefiers were expensive to produce and unreliable in operation.Current liquefiers often involve complex and/or expensive liquefactioncomponents, and often lack safety features to make a liquefaction systemsafer for residential, small-scale, and/or portable use.

For the above-stated reasons, it would be advantageous to provide amethod and apparatus for improving the safety, efficiency, and/or costof producing and storing relatively small quantities of liquefied gas atthe location where the liquefied gas is to be used, such as at an oxygentherapy patient's residence.

SUMMARY

Apparatus and methods for improving the safety and efficiency anddecreasing the cost of producing liquid oxygen with a small-scale useliquefaction device are described. In one embodiment, a liquid oxygenbarrier may be added to an interface between a cryocooler and a dewar tocontrol the rate of liquid oxygen escape upon a tipping of the dewar. Aboiloff tube may be fluidly connected to the dewar to allow expandinggas from a tipped dewar to escape while allowing the liquid to safelysettle in the boiloff tube. A tilt switch may be used to identifywhether a liquefaction device has been tipped or tilted, and to cutelectrical power to the system upon such a condition. The tilt switchmay be a mercury switch, which may be operative to cut electrical powerupon at least a forty-five degree tip or tilt.

In one embodiment, a cold finger of the cryocooler extends within thedewar and may prevent overfilling of the dewar. The cold finger has atemperature gradient with one end having a temperature higher than theboiling point of oxygen and the other end having a temperature lowerthan the boiling point of oxygen. As the gas liquefies and fills thedewar, the liquid level rises only to a level on the cold finger atwhich the temperature exceeds the boiling point of oxygen. At thislevel, no exposed part of the cold finger is cold enough to liquefyoxygen, so the liquid level does not rise further; this may preventoverfilling of the dewar by mechanical, rather than electrical, means.Alternatively, a liquid level sensor may be used to trigger a systemshutdown when the liquid level exceeds a predetermined limit.

In one embodiment, the liquefaction device controls a feed flow ofoxygen using a regulator and orifice to maintain a steady feed flow froman oxygen concentrator. Use of a fixed configuration regulator andorifice allows for the production of USP93 approved liquid oxygen byreceiving USP93 gaseous oxygen from a concentrator and passing it to therest of the system at a steady flow rate. A regulator and orificecombination in a liquefaction device may also be less expensive andeasier to manufacture than a variable flow rate valve, or a variableflow rate valve controlled with a controller in a control loop.

In one embodiment, a compressor in fluid communication with the dewarmay pressurize the dewar to push liquid oxygen out of a transfill tubeand into a portable stroller. This pressurization may be accomplishedusing ambient air. A portable liquid oxygen stroller, with a valveadapted to interface with a transfill valve on the liquefaction device,may be pushed down onto the transfill valve. The portable liquid oxygenstroller may be especially adapted or approved for use with USP93oxygen. This action of placing a portable stroller onto a transfillvalve may activate a transfill switch, which may act to close any fluidoutlets from the dewar except for the transfill tube. The closing of thefluid outlets of the dewar may involve activating a solenoid valve toclose a vent line from the dewar. The transfill switch may also connectto a programmable logic device that terminates the transfill processafter a preset time limit. Pressure relief valves, which may be placedin a feed line and a vent line, may prevent over-pressurization of thedewar or the plumbing of the liquefaction device during a transfillprocess.

In one embodiment, a feed gas flow from a concentrator is separated intotwo flows: one for use by a patient and one for liquefaction. Thepatient flow may be controlled with a patient flowmeter and set to aprescribed limit. The patient flow output may also allow for theconnection of a canula line and a humidifier element.

In one embodiment, a liquefaction device may be held together with amounting shroud. The mounting shroud may include two halves. The twohalves may include a clamping element configured to encompass both acryocooler flange and a dewar flange, with an O-ring placed between thecryocooler flange and the dewar flange. When the mounting shroud, andthus the clamping element, is closed, the clamping element providesopposing axial forces to push the cryocooler flange and dewar flangetogether to compress the O-ring. This creates a seal between thecryocooler flange and the dewar flange, preventing leakage of gaseous orliquid oxygen even when the liquefaction device is tipped over. Themounting shroud may also secure the dewar and cryocooler into a chassisassembly. Vibration dampeners may be mounted between the mounting shroudand chassis to ameliorate noise and vibration. A cooling fan may besecured to the mounting shroud to allow cooling of a cryocooler fin andof electrical components. The mounting shroud design itself may providean enclosed air path to route air through a cooling fin of thecryocooler, reducing the likelihood that the cryocooler overheats orsuffers a seized displacer.

In one embodiment, a liquefaction device employs a stainless steel dewarwith a bellows neck. A metal dewar with a metal neck tube may be moredurable than either a glass dewar or metal dewar with a composite necktube. A metal neck tube reduces flammability concerns due to the highoxygen environment. An all-metal dewar construction allows for thewelding of a mounting flange directly to the top of the dewar, which, inturn, allows for a better seal between the dewar and a cryocoolerflange. A bellows neck design reduces thermal conductivity and furtherreduces heat loss from inside the dewar. Such a dewar design providesease of manufacture and a reduction in the number of necessary assemblyparts.

Devices for transferring liquid gas from a storage dewar to a portabledewar are provided, according to various embodiments of the presentinvention. Such embodiments of devices may include a storage dewaroperable to contain a liquid gas for portable medical gas therapy, atransfill tube having a first end and a second end, the first endextending within the storage dewar, the second end opening outside ofthe storage dewar, a valve coupled to the second end, a means forpressurizing the storage dewar to push the liquid gas through thetransfill tube, and a switch electrically coupled to the means forpressurizing the storage dewar, the switch located relative to the valveso as to automatically activate the means for pressurizing the storagedewar upon engagement of a portable dewar to the valve. In someinstances of the embodiments, the means for pressurizing the storagedewar may be a compressor in fluid communication with the storage dewar.In some cases, the compressor may pressurize the storage dewar withambient air. Other instances of the embodiments may further include avent tube in fluid communication with the storage dewar and configuredto permit gases to exit the storage dewar. In such instances, the venttube may include a solenoid valve, and the switch may be configured toclose the solenoid valve upon activating the compressor. Embodiments ofthe devices may include a timing device operable to deactivate thecompressor after a predetermined time. The predetermined time, may be,for example, two minutes.

According to some embodiments of the devices, the valve and the switchare mounted on a housing, and the housing has formed therein adepression shaped to fit a valve interface surface of the portabledewar. In some cases, the switch may be a push-button switch configuredto be pressed by the portable dewar when the portable dewar has beenengaged with the valve. In other cases, the switch may be a proximitydetection switch configured to trigger when the portable dewar is closeenough to be engaged with the valve. In yet other cases, the valve is afirst valve and the portable stroller may include a second valve. Insuch cases, the first valve may be configured to engage the second valvesuch that pushing the second valve onto the first valve opens the firstand second valves. Embodiments of the devices may farther include acryocooler with a cold finger, the cold finger extending within thestorage dewar and operable to liquefy gas for containment in the storagedewar.

A method of maintaining oxygen purity in liquefaction of gas forresidential oxygen therapy is provided, according to various embodimentsof the present invention. Such embodiments of methods may includereceiving a feed stream of gas from an oxygen concentrator, providing acryocooler having a cold finger, the cold finger extending within acontainer and operable to liquefy the gas for containment in thecontainer, maintaining the cold finger at a substantially constanttemperature at or below the liquefaction temperature of oxygen,liquefying at least part of the feed stream of gas, the oxygen purity ofliquefied gas being substantially at or greater than the oxygen purityof the feed stream of gas, drawing the feed stream of gas to the coldfinger at least in part with a low pressure created by liquefaction ofthe feed stream of gas at a surface of the cold finger, and accumulatingthe liquefied gas in the container. Maintaining the cold finger at asubstantially constant temperature may include supplying a constantelectrical power to the cryocooler and receiving the feed stream of gasat a substantially constant rate. The substantially constant temperaturemay be, for example, approximately equal to eighty-seven degrees Kelvin.In some cases, the oxygen purity of the liquefied gas may be ninety toninety-six percent by volume; in other cases, the oxygen purity of theliquefied gas may be approximately ninety-three percent by volume; inyet other cases, the oxygen purity of the liquefied gas is at leastninety-nine percent by volume. Embodiments of the methods may furtherinclude providing a portable dewar operable to store the liquefied gasfor ambulatory medical gas therapy and transferring the liquefied gasfrom the container to the portable dewar.

A method for reducing power consumption in residential medical gasliquefaction and storage is provided, according to various embodimentsof the present invention. Such embodiments may include receiving a feedstream of gas from an oxygen concentrator, providing a cryocooler havinga cold finger, the cold finger extending within a container and operableto liquefy at least part of the feed stream of gas for containment inthe container, mounting a liquid level sensor within the container, theliquid level sensor operable to detect a liquid level in the container,and initiating a low power mode of the cryocooler when the liquid levelreaches a predetermined liquid level. In some cases, the predeterminedliquid level may be a full liquid level. In other cases, thepredetermined liquid level may be a first predetermined liquid level,and initiating the low power mode of the cryocooler may further includereducing a power supply of the cryocooler to a predetermined low powersetting, and restoring the power supply of the cryocooler to apredetermined full power setting when the liquid level has dropped to asecond predetermined liquid level. In some cases, the secondpredetermined liquid level may be a three-fourths full liquid level.

Initiating the low power mode of the cryocooler, according to variousembodiments of the present invention, may further include providing acooling fan operable to remove heat from the cryocooler, reducing apower supply of the cooling fan to another predetermined low powersetting, and restoring the power supply of the cooling fan to anotherpredetermined full power setting when the liquid level has dropped tothe second predetermined liquid level. Initiating the low power mode ofthe cryocooler, according to various alternative embodiments of thepresent invention, may include selecting a maintenance temperature forthe cold finger needed to maintain the liquid level at full, monitoringa temperature of the cold finger, and varying a power supply of thecryocooler to maintain the temperature at the maintenance temperature.Embodiments of the methods may exclude varying pressure within thecontainer or flow rate of the feed stream of gas during liquefaction. Insome cases, the liquid level sensor may be a capacitive-type liquidlevel sensor.

An apparatus for passively stalling liquefaction is provided, accordingto various embodiments of the present invention. Such embodiments mayinclude a container operable to contain liquid oxygen for portableoxygen therapy and a cryocooler comprising a cold finger, the coldfinger extending vertically within the container and operable to liquefyoxygen gas for containment in the container, the cold finger comprisinga cold end portion cold enough to liquefy the oxygen gas and a secondportion too warm to liquefy the oxygen gas, the cold end portionextending entirely within the container and the second portion extendingat least partially within the container such that liquefaction stalls assoon as the liquid oxygen gas in the container submerges the cold endportion. According to such embodiments, the temperature along the coldfinger may vary according to a temperature gradient, the cold fingerhaving a highest temperature closest to the cryocooler and a lowesttemperature furthest from the cryocooler.

A device for transferring liquid gas from a storage dewar to a portabledewar is provided, according to various embodiments of the presentinvention. Such embodiments may include a first dewar configured tocontain a liquid gas of a certain purity range for portable medical gastherapy, a female transfill valve associated with the first dewar, asecond dewar configured to contain a liquid gas of the certain purityrange for portable medical gas therapy, a male transfill valveassociated with the second dewar, and a transfill tube having a firstend and a second end, the first end extending within the second dewar,the second end in fluid communication with the male transfill valve.According to such embodiments, the male transfill valve may beconfigured to be incompatible with an other dewar not configured tocontain a liquid gas of the certain purity range.

Other features of embodiments of the present invention will be apparentfrom the accompanying drawings and from the detailed description thatfollows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a cross-section, cut-away view of the cryocooler anddewar interface of one embodiment of the present invention.

FIG. 2 depicts a cross-section, cut-away view of the cryocooler anddewar of one embodiment of the present invention, showing a possibleplacement of temperature sensors.

FIG. 3 depicts a cross-section, cut-away view of one embodiment of aliquid oxygen barrier situated within the cryocooler and dewar interfaceof one embodiment of the present invention.

FIG. 4 depicts a cross-section, cut-away view of the cryocooler anddewar interface of one embodiment of the present invention, showing amaximum sustainable liquid oxygen level in the dewar.

FIG. 5 depicts a conceptual system diagram of one embodiment of thepresent invention coupled to an oxygen concentrator, illustrating liquidflow during a liquefaction cycle.

FIG. 6 depicts a conceptual system diagram of one embodiment of thepresent invention coupled to an oxygen concentrator, illustrating liquidflow during a transfill cycle.

FIG. 7 depicts a side view of a liquid level sensor of one embodiment ofthe present invention.

FIG. 8 depicts a cross-section, cut-away view of a dewar of oneembodiment of the present invention, showing the placement therein ofthe liquid level sensor of FIG. 7.

FIG. 9 depicts a perspective view of a lower chassis assembly of aliquefaction device according to one embodiment of the presentinvention.

FIG. 10 depicts another perspective view of a lower chassis assembly ofone embodiment of the present invention.

FIG. 11 depicts another perspective view of a lower chassis assembly ofone embodiment of the present invention.

FIG. 12 depicts a perspective view of the outer housing of aliquefaction device according to one embodiment of the presentinvention, showing a possible placement of a detachable humidifier.

FIG. 13 depicts a partial cross-sectional view of the outer housing witha transfill valve and a transfill switch, and a portable stroller with afemale valve, according to one embodiment of the present invention.

FIG. 14 depicts a top perspective view of the outer housing of aliquefaction device according to one embodiment of the presentinvention, showing one embodiment of a transfill valve and transfillswitch.

FIG. 15 depicts a side perspective view of a cryocooler and dewarsecured by a mounting shroud to an upper chassis of a liquefactiondevice according to one embodiment of the present invention.

FIG. 16 depicts a perspective view of a mounting shroud and dewaraccording to one embodiment of the present invention.

FIG. 17 depicts a side perspective view similar to FIG. 16, with themounting shroud shown in cut-away view.

FIG. 18 depicts a side perspective view of a cryocooler/dewar flangeinterface with a cut-away view of a mounting shroud.

FIG. 19 depicts a side perspective, cut-away view of an inside of acryocooler and dewar interface of one embodiment of the presentinvention, showing one embodiment of a cold finger and a liquid oxygenbarrier.

FIG. 20 depicts a side perspective view of a liquid oxygen barrier andflow director, according to one embodiment of the present invention.

FIG. 21 depicts a side perspective, cut-away view of an inside of acryocooler and dewar interface of one embodiment of the presentinvention, showing an embodiment of a cold finger and a liquid oxygenbarrier and flow director.

FIG. 22 depicts a side view of a dewar according to one embodiment ofthe present invention.

FIG. 23 depicts a partial view of a conceptual system diagram similar tothe conceptual system diagram of FIG. 5, according to some embodimentsof the present invention.

FIG. 24 illustrates a partial cross-sectional view of a male transfillvalve and female valve interface, according to some embodiments of thepresent invention.

FIG. 25 depicts a conceptual wiring diagram for an impact-sensingmechanism to turn off electrical components of a liquefaction system,according to various embodiments of the present invention.

FIG. 26 depicts a conceptual wiring diagram for a tip-over switch toturn off electrical components of a liquefaction system, according tovarious embodiments of the present invention.

FIG. 27 depicts a conceptual wiring diagram for a temperature sensingcircuit to turn off electrical components of a liquefaction system,according to various embodiments of the present invention.

FIG. 28 depicts a conceptual wiring diagram for measurement of oxygenpurity and display options for displaying oxygen purity, according tovarious embodiments of the present invention.

FIG. 29 depicts a conceptual wiring diagram for a transfill switch forcompleting a compressor power circuit and/or a solenoid power circuit,according to various embodiments of the present invention.

FIG. 30 depicts a transfill time-out flow chart, according to variousembodiments of the present invention.

FIG. 31 depicts a conceptual wiring diagram illustrating a cryocoolerlow power mode, according to various embodiments of the presentinvention.

FIG. 32 depicts a conceptual wiring diagram illustrating a cooling fanlow power mode, according to various embodiments of the presentinvention.

FIG. 33 depicts a conceptual wiring diagram illustrating a cooling fanlow power mode, according to various embodiments of the presentinvention.

FIG. 34 depicts a flow diagram illustrating a method for maintainingoxygen purity in liquefaction of gas, according to various embodimentsof the present invention.

FIG. 35 depicts flow diagrams illustrating a method for reducing powerconsumption in residential medical gas liquefaction and storage and amethod for initiating a low power mode of a cryocooler, according tovarious embodiments of the present invention.

FIG. 36 depicts flow diagrams illustrating methods for initiating a lowpower mode of a cryocooler, according to various embodiments of thepresent invention.

DETAILED DESCRIPTION

In recent years, cryocoolers have been intensively developed. Initially,cryocoolers were developed for the military for use in such applicationsas cooling infrared sensors, semiconductor chips, microwave electronics,high temperature superconductivity applications, fiber optic amplifiers,etc. The cryocoolers developed for these applications operated in atemperature range of from about 20K to 150K, and their cooling capacityranged from less than a watt to over 100 watts. In addition, thecryocoolers developed for the above-described military applicationsprovided their heat input at or near the lowest temperature point of thecryocooler. For instance, the component to be cooled was typicallyattached to the cold point (the “cold finger”) of the cryocooler,transferring heat directly to that component, with minimal conductionlosses. However, for use in small scale gas liquefiers, features such asprecise control of each parameter of liquefaction and quick cool downare not necessary, and serve only to increase the cost of the device.

With respect to the need for relatively small but steady quantities ofoxygen by patients on oxygen therapy, there have been several ways inwhich the needs of such patients have been met. The most common methodfor oxygen therapy patients to receive oxygen is through regulardeliveries of oxygen produced at a commercial plant. The oxygen may bedelivered as either a pressurized gas or as a liquid. When delivered asa pressurized gas, the oxygen presents a hazard because of the highpressure under which it is stored and because oxygen is highly reactive.Oxygen delivered as a liquid is subject to losses resulting fromboil-off, which occurs due to the inevitable warming of the liquefiedgas over time. Because such losses occur even when specially insulatedcontainers, or dewars, are used, deliveries of fresh liquid oxygen mustbe made on a weekly basis.

It is also known to provide devices which extract or concentrate oxygenfound in the ambient air. These devices obviate the need to store apotentially hazardous material. However, these devices are typically notportable, and therefore a person on continuous oxygen therapy must oftenrely on oxygen that has been “bottled” commercially in order to leavehis or her residence.

In recent years, some advances have been made toward producing home-useoxygen liquefaction devices. Examples of such devices may be found inU.S. Pat. No. 5,893,275, entitled “Compact Small Volume Liquid OxygenProduction System,” filed on Sep. 4, 1997, and U.S. Pat. No. 6,212,904,entitled “Liquid Oxygen Production,” filed on Nov. 1, 1999, of which thecontent of each is herein incorporated by reference in its entirety.

Some prior gas liquefaction devices have typically employed complexand/or expensive condenser structures. It has previously been thoughtadvantageous to force a feed gas stream across a cold surface in orderto improve liquefaction efficiency. It has also previously been thoughtadvantageous to employ a cooled structure, such as a double-walledcondenser structure attached to a cold surface of the cryocooler, and todirect the feed gas through the condenser structure to increase surfacearea over which liquefaction occurs.

Additionally, home-use oxygen liquefaction devices often lack safetymechanisms to prevent injury or damage when the device is tipped ontoits side or overheats. Liquid oxygen escaping from a tipped storagedewar can expand and boil rapidly as it encounters warm surfaces,causing vast amounts of liquid oxygen to spray or shoot rapidly throughan exhaust vent. If the liquefaction device's electrical power remainson during a tip, escaping oxygen can also cause a fire hazard if itencounters spark or flame. Overheating components may also damage aliquefaction device. In liquefaction devices employing cryocoolers, thecryocooler can overheat or suffer a seized displacer. Overfilling aliquid oxygen storage dewar may also be hazardous; some oxygenliquefaction devices rely on an electronic controller to stop liquidoxygen production. Other safety concerns involve the transfilling of aportable liquid oxygen stroller from another dewar; this process maysometimes cause portions of a portable liquid oxygen stroller to freezeonto a connection to another dewar, resulting in an overfill of theportable stroller or an over-emptying of the dewar.

Because medical oxygen may be considered a prescription drug, it may beregulated by a government agency. For instance, the Federal DrugAdministration (FDA) in the United States regulates oxygen liquefactiondevices. Resources have been expended for United States Pharmacopeia(USP) approved oxygen liquefaction devices. USP approved devices produceoxygen that is approximately 99.0% pure; USP93 approved devices produceoxygen that is 93% pure, within a ±3% tolerance. USP approved devicesoften seek, at higher cost, to optimize the oxygen liquefaction processto achieve an approximate 99.0% purity. This may be done through the useof an advanced feedback and control loop that varies the flow rate of afeed gas containing oxygen. However, the necessary sensors andcontrollers used for such an optimization process can be expensive.

In the present application, apparatus and methods for improving thesafety and efficiency and decreasing the cost of producing liquid oxygenwith a small-scale use liquefaction device are described. Variousterminology is used herein to refer to one or more aspects ofembodiments of the present invention. A “residential,” “small-scaleuse,” or “portable” liquefaction device refers to a liquefaction deviceoperable to produce as much as twenty-five liters of liquid gas per day;typically, such devices produce small-scale amounts of liquid gas in therange of approximately 1.5 liters of liquid gas in a twenty-four hourperiod. As used herein, the terms “boiloff vessel” and “phase separator”are used interchangeably, and are used in their broadest sense to referto any container able to receive a rapidly-expanding mixture of gas andliquid gas to separate the gas and liquid phases by allowing the liquidgas to fall to the bottom of the container and boil off gradually whilepermitting the gas to exit the container. “Boiloff tube” refers to oneparticular embodiment of a boiloff vessel configuration. As used herein,the term “dewar” is used in its broadest sense to refer to a container,for example a cryogenically-insulated container, operable to receiveand/or store a liquid gas, for example liquid oxygen. As used herein,the terms “portable dewar,” “stroller,” and “portable stroller” are usedinterchangeably, and are used in their broadest sense to refer to acontainer, for example a cryogenically-insulated container, operable toreceive and/or store a liquid gas, for example liquid oxygen, in a waythat permits the container to be carried, carted, or the like forambulatory medical gas therapy.

As used herein, the term “in fluid communication” is used in itsbroadest sense to refer to elements related in a way that permits fluidto flow between them, either indirectly via another element, ordirectly. As used herein, the terms “feed tube” and “feed line” and“feed hose” are used interchangeably, and are used in their broadestsense to refer to any fluid flow mechanism operable to convey gas from aconcentrator to a cryocooler and/or dewar. As used herein, the terms“vent tube” and “vent line” and “vent hose” are used interchangeably,and are used in their broadest sense to refer to any fluid flowmechanism operable to convey gas away from a cryocooler and/or dewar. Asused herein, the term “heat dissipator” is used in its broadest sense torefer to a thermal mechanism operable to receive heat from one area andrelease it in another area. One example of an embodiment of a heatdissipator is a cryocooler cooling fin. As used herein, the indefinitearticles “a” or “an” are used in their traditional senses to refer toone or more of an element. As used herein, the phrases “in oneembodiment,” “according to one embodiment,” and the like generally meanthat the particular feature, structure, or characteristic following thephrase is included in at least one embodiment of the present invention,and may be included in more than one embodiment of the presentinvention. Importantly, such phases do not necessarily refer to the sameembodiment.

With reference to FIG. 5, a conceptual system diagram of one embodimentof the present invention coupled to an oxygen concentrator, illustratingliquid flow during a liquefaction cycle, is depicted. Oxygenconcentrator 530 outputs a flow of concentrated oxygen. In FIG. 5, “FFF”refers to the presence of oxygen feed flow, “PPP” refers to the presenceof patient gaseous oxygen flow, and “VVV” refers to the presence of ventgas flow. A typical concentrator 530 may output between approximatelyfive and ten liters of oxygen per minute. In one embodiment, oxygenconcentrator outputs a flow of USP93 approved oxygen. According to someembodiments of the present invention, the output flow rate of oxygenconcentrator 530 may be set to its maximum value. From the oxygenconcentrator 530, the output flow branches into a feed flow line 512“FFF” and a patient flow line 534 “PPP.” The patient flow passes througha patient orifice 536. The patient orifice 536 may be configured toprevent the patient flow line 534 from “robbing” the feed flow line 512,or in other words allowing too much of the concentrator's 530 outputflow to pass through the patient flow line 534 and not enough to passthrough the feed flow line 512. After passing through the patientorifice 536, the patient flow passes through a patient flowmeter 538,which allows the patient to adjust the flow rate of oxygen received fromthe patient flow line 534. In one embodiment, the patient flowmeter 538comprises a variable orifice in the form of a needle valve. The patientflow line 534 may provide a connection port similar to those found on anoxygen concentrator, allowing for the connection of a canula line or ahumidifier bottle if desired.

In one embodiment, the feed gas flow rate in the feed flow line 512 ismaintained at a constant rate by pressure regulator 540 and orifice 542.The oxygen concentrator 530 typically has an outlet pressure of aboutsix to eight pounds per square inch gauge (PSIG). The pressure regulator540 operates to reduce the pressure of the feed flow. In one embodiment,the pressure of the feed flow is reduced to 3.8 PSIG. After passingthrough regulator 540, the feed flow passes through an orifice 542. Inone embodiment, the orifice 542 has a diameter of 0.016 inches. Anoxygen feed flow at a pressure of 3.8 PSIG will pass through an orificeof 0.016 inch diameter at a rate of approximately 1.25 liters perminute. According to some embodiments of the present invention, apressure regulator 540 and orifice 542 combination permit a constantfeed flow rate of oxygen gas to be supplied for liquefaction.Alternatively, various other fixed flow rates may be achieved throughthe selection of different pressure regulators 540 and/or orifices 542of different sizes.

A liquefaction device employing a fixed pressure regulator 540 and afixed diameter orifice 542 has advantages over a system employing avariable flow control feedback loop, such as those employing a variablevalve with a controller. For instance, a regulator 540 and orifice 542combination may cost less and may be easier to manufacture than avariable flow system. In one embodiment using a regulator 540 andorifice 542 combination, concentrated USP93 oxygen from an oxygenconcentrator 530 may simply be regulated to a fixed pressure and sentthrough a fixed diameter orifice that sends a steady flow of USP93oxygen gas to be liquefied as USP93 oxygen.

Next, the feed flow passes through a one-way check valve 544 and intodesiccant cartridge 550. According to some embodiments of the presentinvention, desiccant cartridge 550 is an optional element. In oneembodiment, desiccant cartridge 550 is a removably attachable desiccantcartridge for dehumidifying a gas feedstream in a portable gasliquefying apparatus. Preferably, the desiccant cartridge 550 is compactand portable. The desiccant cartridge 550 may reduce or prevent rimeformation and reduce moisture content to increase overall efficiency ofthe liquefaction apparatus.

In one embodiment, the desiccant cartridge comprises a gas feedstreaminlet, a dehumidifying zone in communication with the gas feedstreaminlet, and a dehumidified gas feedstream outlet in communication withthe dehumidifying zone. The gas feedstream inlet may be adapted toreceive a gas feedstream from a gas feedstream generating device, suchas oxygen concentrator 530. The dehumidified gas feedstream outlet maybe adapted to allow transfer of the dehumidified gas feedstream to acryogenic unit. Various embodiments of desiccant cartridge 550 aredescribed in greater detail in U.S. patent application Ser. No.10/884,318 entitled “Desiccant Cartridge,” filed on Jul. 1, 2004, thecontents of which are hereby incorporated by reference in theirentirety.

After passing through desiccant cartridge 550, the feed flow mayoptionally pass through a filter 552. In one embodiment, filter 552 is aten micron filter. The feed flow may then enter the cryocooler 502 nearthe cryocooler 502/dewar 520 interface, through the feed flow tube 512.The feed flow passes by cold finger 508 and is liquefied, thereafterfalling into dewar 520. Boiloff gas and/or a portion of the feed flowthat has not been liquefied may create a vent flow (VVV) that may leavethe dewar 520 and flow out of vent tube 514. The vent flow may next passthrough a normally-open solenoid valve 556 and into a boiloff tube 560.From the boiloff tube 560, the gas exits the system to the atmosphere.

In one embodiment, boiloff tube 560 increases the safety of aliquefaction device. Even with use of a liquid oxygen barrier 118,liquid oxygen may still flow out of a dewar 520 if the dewar 520 istipped over. The boiloff tube 560 may work in conjunction with theliquid oxygen barrier 118 to prevent liquid oxygen from spraying out ofthe vent port of a liquefaction apparatus upon tipping of the apparatus.Upon tipping, as liquid oxygen flows through the feed line 512 and ventline 514, its volume may expand by a ratio of about 800 times as itboils into gas which, in turn, may push the remaining liquid forward aspressure builds. Boiloff tube 560 may provide a volume in which theremaining liquid may drop out of the way to allow the gas to vent fromthe liquefaction apparatus without pushing liquid through the vent portand out of the system. This may, in turn, minimize potential humancontact with a rapidly-expanding mixture of oxygen gas and liquidoxygen. In one embodiment, the boiloff tube 560 comprises a wide sectionof tubing that, when laying on its side, provides a section in whichliquid may pool. Liquid pooled inside the boiloff tube 560 will boil offto gas and safely vent from the boiloff tube 560. In one embodiment,boiloff tube 560 is constructed with PVC pipe.

FIG. 23 depicts a partial view of a conceptual system diagram similar tothe conceptual system diagram of FIG. 5, according to some embodimentsof the present invention. As with FIGS. 5 and 6, although theconfiguration of elements in FIG. 23 does not necessarily depict thespatial relationship between elements such as scale or distance, FIG. 23represents the directional orientation relationship between dewar 2320,cold finger 2308, cryocooler 2301, and boiloff vessel 2385. Boiloffvessel 2385 is an alternative embodiment. The “bottom” of boiloff vessel2385 is the surface of boiloff vessel 2385 toward which liquid would bepulled by gravity; the location of the “bottom” may vary according tothe orientation of boiloff vessel 2385. When dewar 2320 and boiloffvessel 2385 are in an upright position, the force of gravity acts in adirection similar to the direction of arrow 2302. In the uprightposition, liquid gas is contained at the bottom of dewar 2320, and ventgas (such as boiloff gas and/or non-liquefied feed flow gas) passes outof dewar 2320 and/or cryocooler 2301 through vent line 2314, throughnormally-open solenoid valve 2356, into boiloff vessel 2385, and outthrough boiloff vent 2387. According to some embodiments of the presentinvention, atmospheric gases, such as ambient air, may be prevented fromentering boiloff vessel 2385, cryocooler 2301, and/or dewar 2320 throughan open vent line, such as boiloff vent 2387, by maintaining a positiveflow of feedstream gas through feed line 2312 to cold finger 2308.

Dewar 2320, cryocooler 2301, and boiloff vessel 2385 may be tippedand/or tilted into a least favorable position, in which gravity acts ina direction similar to the direction of arrow 2306. In such cases,liquid gas within dewar 2320 may contact parts of dewar 2320, cryocooler2301, and/or cold finger 2308 that are at or warmer than the boilingpoint of the liquid gas, causing the liquid gas to evaporate and/orexpand. This rapidly-expanding mixture of gas and liquid gas maypressurize the dewar, causing the rapidly-expanding mixture to quicklyflow out of the dewar 2320/cryocooler 2301 interface through feed line2312 and/or vent line 2314. In the least favorable position in whichgravity acts in the direction 2306, gravity further pulls the liquid gasthrough the warm feed line 2312 and/or vent line 2314. Therapidly-expanding mixture that passes through feed line 2312 may beprevented from flowing back to concentrator 530 with a one-way checkvalve 544 or to compressor 646 with one-way check valve 648. Instead,the rapidly-expanding mixture that passes through feed line 2312 mayflow through relief line 2395 through pressure relief valve 2354 andinto boiloff vessel 2385 via opening 2393. The rapidly-expanding mixturethat passes through vent line 2314 may pass through solenoid valve 2356and into boiloff vessel 2385 via opening 2391. Alternatively, ifsolenoid valve 2356 is closed or if solenoid valve 2356 does not permitenough of the rapidly-expanding mixture to pass through, then themixture may pass through relief line 2399 through pressure relief valve2358 and into boiloff vessel 2385 via opening 2391. Opening 2389 opensto atmosphere; for example, opening 2389 opens from boiloff vessel 2385to atmosphere via boiloff vent 2387.

As the rapidly-expanding mixture of gas and liquid gas enters boiloffvessel 2385 via opening 2391 and/or 2393, the liquid phase of themixture of gas and liquid gas may settle to the bottom of boiloff vessel2385, and the gas phase of the mixture of gas and liquid gas may exitboiloff vessel 2385 via opening 2389. According to some embodiments ofthe present invention, the mixture of gas and liquid gas may spray intoboiloff vessel 2385 toward the side of boiloff vessel 2385 that opposesopening 2391 and/or 2393. According to some embodiments of the presentinvention, boiloff vessel 2385 has an elongated cylindrical shape, andopening 2389 may be placed in proximity to or near the end closest tohole 2391 and/or 2393. Such a configuration may permit boiloff vessel2385 and/or dewar 2320 to be uprighted shortly after a tipping eventwithout permitting the liquid within boiloff vessel 2385 to spray out ofboiloff vent 2387 and/or hole 2389. According to some embodiments of thepresent invention, having opening 2389 near the end of boiloff vessel2385 and near opening 2391 and/or opening 2393 may permit the greatestliquid capacity while keeping boiloff vessel 2385 size as small aspossible. Depending on the shape and configuration of boiloff vessel2385, and the positioning of holes 2391, 2393, and/or 2389, the size ofboiloff vessel 2385 should be selected to accommodate the proper amountof liquid. For example, according to one embodiment of the presentinvention, the volume of boiloff vessel 2385 is approximately equal toone-third of the volume of liquid in the dewar corresponding to a fullliquid level. As another example, if a liquid gas dewar holdsapproximately 1.5 liters of liquid gas, a boiloff vessel 2385 with avolume of approximately 0.5 liters may be used. Alternatively, thevolume of boiloff vessel 2385 may be approximately equal to one-half ofthe volume of liquid in the dewar corresponding to a full liquid level,according to some embodiments of the present invention.

Dewar 2320, cryocooler 2301, and boiloff vessel 2385 may be tippedand/or tilted into a position in which gravity acts in a directionsimilar to the direction of arrow 2304. According to some embodiments ofthe present invention, in such cases the length of vent tube 2314 and/orvent tube 2387 may permit the liquid gas to boil off before any of itexits opening 2389 and/or boiloff vent 2387 in the liquid phase,particularly because gravity does not act in such cases to pull liquidgas down into feed flow line 2312 and/or vent line 2314. Dewar 2320,cryocooler 2301, and boiloff vessel 2385 may also be tipped and/ortilted into a position in which gravity acts in a directionperpendicular to the directions indicated by arrows 2302, 2304, 2306. Insuch cases, feed tube 2312 and flow tube 2314 may extend to the side andmay permit a moderate volume of liquid gas to escape dewar 2320 withapproximately half the volume of boiloff vessel 2387 available tocontain the liquid gas while it boils off, while leaving a fluid pathfor vent gas to escape through opening 2389.

Although boiloff vessel 2385 is shown with openings 2391, 2393, and2389, boiloff vessel 2385 may alternatively be configured with opening2389 and either opening 2391 or opening 2393, according to variousembodiments. Alternatively locating opening 2389 on an end of boiloffvessel 2385 opposite from opening 2391 and/or opening 2393 (such asdepicted with boiloff vessel 560) may permit boiloff vessel 2385 tocontain the liquid gas uniformly in any direction of tipover; however,locating opening 2389 on an end of boiloff vessel 2385 opposite fromopening 2391 and/or opening 2393 may result in liquid gas traveling outof boiloff vent 2387 when boiloff vessel 2385 is uprighted directlyfollowing a tipover event.

Although openings 2391, 2393, and 2389 are depicted as small holes sizedto accommodate flow through a tube, openings 2391, 2393, and/or 2389 maybe varied in size and shape. According to some embodiments of thepresent invention, multiple boiloff vessels may be used. Althoughboiloff vessels 560, 660, 2385 are depicted as cylinders, boiloffvessels according to embodiments of the present invention may be anyshape that permits holding or enclosure of a volume of cryogenic liquid;for example, boiloff vessels according to embodiments of the presentinvention may be, but are not limited to, spheres, cubes, boxes,U-shaped volumes, cylinders, semi-spheres, semi-cylinders, pyramids,cones, semi-pyramids, semi-cones, and/or toroids. According to someembodiments of the present invention, a boiloff vessel surrounds aportion or all of dewar 2320; such a boiloff vessel configuration maysave space in some cases. Based on the disclosure provided herein, oneof ordinary skill in the art will appreciate a number of differentpossible shapes, sizes, and configurations of boiloff vessels accordingto various embodiments of the present invention.

FIG. 6 illustrates a system similar to the system of FIG. 5, during atransfill cycle according to embodiments of the present invention. Inone embodiment, a compressor 646 is used to pressurize the dewar 620 andthus the feed line 612 in order to perform a transfill of liquid oxygenfrom dewar 620 to portable stroller 668. To commence transfill,compressor 646 is turned on. In FIG. 6, “PPP” refers to the presence ofpatient gaseous oxygen flow, “HHH” refers to the presence of gas flow,such as ambient air flow, from compressor 646, and “LLL” refers to thepresence of liquid gas flow, such as liquid oxygen flow.

In order to keep the system pressure low in the dewar 620 during liquidoxygen production, the vent line 614 is open to atmosphere. Backflow ofambient air into the dewar 620 is avoided by maintaining a slightlypositive flow of gaseous oxygen to the cryocooler 602, and by includinga one-way check valve 599 in the vent line 614. However, transfill ofliquid oxygen requires an elevated pressure in the dewar 620. Therefore,a normally-open solenoid valve 656 is closed during transfill in orderto permit a pressure buildup inside dewar 620. A transfill tube 662connects a transfill valve 664 outside the dewar 620 to the inside ofthe dewar 620; one end of transfill tube 662 extends within dewar 620,another end extends outside of dewar 620. In one embodiment, transfilltube 662 is made of metal and passes through the two walls and vacuumspace of an insulated dewar 620.

Compressor 646 draws in ambient air, compresses it, and sends it throughone-way check valve 648. Check valves 644, 648 substantially preventcompressed air from backing up into the compressor 646, into theconcentrator 630, or into the patient flow. For example, check valve 644may not only prevent a backflow into the concentrator 630 duringliquefaction or transfill, but may also prevent an over-feed of thepatient supply 634. Check valve 544 may perform similar functions.During transfill, flow of gaseous oxygen from the concentrator 630continues to pass through patient flow line 634, through patient orifice636, and through patient flowmeter 638. As compressor 646 continues todraw ambient air into the feed line 612, a space above the liquid in thedewar becomes pressurized, creating a downward force on the top of theliquid that pushes liquid out of the dewar 620 and into the transfilltube 662. The liquid then passes through transfill valve 664 into aportable oxygen stroller 668.

In addition to compressor 646, other means may be used to pressurizedewar 620 for a transfill process. For example, a heater may be placedwithin dewar 620 to boil oxygen until enough pressure builds up in dewar620 to push liquid from dewar 620 through transfill tube 662. As anotherexample, a heat source may be situated near, but not inside, of dewar620, such that enough heat may be supplied through the heat source tobuild pressure within dewar 620. As yet another example, a vaporizerloop or controllable heat leak may be used to raise the pressure withindewar 620 for a transfill process.

In one embodiment, the transfill process begins when the stroller 668 isaligned with the transfill valve 664 and pushed onto the transfill valve664; a transfill switch 666 may be configured to activate when thestroller 668 is engaged with the transfill valve 664. According to someembodiments of the present invention, transfill switch 666 is apush-button switch that may be pushed or pressed by a valve interfacesurface 697 of portable stroller 668 when portable stroller 668 has beenengaged with valve 664. According to other embodiments, transfill switch666 is a proximity detection switch configured to trigger when theportable stroller 668 is close enough to valve 664 to be engaged withvalve 664. Transfill switch 666 may activate compressor 646 and closesolenoid valve 656. In one embodiment, the transfill of liquid oxygen toa portable stroller may be activated through a state change on the inputof a programmable logic device, which may operate to activate thecompressor 646, close the solenoid valve 656, monitor the time sincetransfill began, and terminate the transfill after a predetermined time.This may prevent an over-emptying of the dewar 620 and may minimizeoverfilling of the portable stroller 668 during transfills, in which thestroller 668 sometimes freezes to the transfill valve 664 and prevents auser from manually ending the transfill process by removing the stroller668 from the transfill valve 664 and transfill switch 666.

In one embodiment, portable stroller 668 is a USP93 approved stroller.The stroller 668 is a device that a patient uses to carry liquid oxygen.Oxygen concentrators are currently approved for USP93 oxygen, but theyproduce gaseous oxygen. Oxygen in a liquid form may appeal most to apatient because liquid is the most convenient state of oxygen forportable use. A patient can carry a greater amount of oxygen in asmaller and lighter container than would exist for a comparable amountof gaseous oxygen. Portable stroller 668 may boil off liquid oxygen at aprescribed rate to provide a flow of breathable oxygen to a patient.

In one embodiment, pressure relief valves 654, 658 prevent anover-pressurization of the dewar 620. Relief valve 654 connects feedline 612 to boiloff tube 660, and relief valve 658 connects vent line614 to boiloff tube 660. Alternatively, pressure relief valve 654 may beplaced inline with a pressure relief line 698, the pressure relief line698 having a first end in fluid communication with the feed line 612,and having a second end in fluid communication with boiloff tube 660. Inone embodiment, pressure relief valve 654 can be configured to open whenpressure in the feed line 612 equals a predetermined pressure, such astwelve PSIG, with a tolerance of 10%, thereby permitting the highpressure fluid to flow out of feed line 612, through pressure reliefline 698, and into boiloff tube 660. In some embodiments, pressurerelief valve 658 may be placed inline with a pressure relief line 699.Pressure relief line 699 may have a first end in fluid communicationwith vent line 614, and a second end in fluid communication with boilofftube 660. Alternatively, the second end of pressure relief line 699 mayalso be in fluid communication with vent line 614. For example, inembodiments in which vent line 614 comprises solenoid valve 656,pressure relief line 699 may simply bypass solenoid valve 656 in ventline 614. In one embodiment, pressure relief valve 658 can be configuredto open when pressure in the vent line 614 exceeds a predeterminedpressure, such as twelve PSIG, with a tolerance of 10%, therebypermitting the high pressure fluid to flow out of vent line 614, throughpressure relief line 699, and into boiloff tube 660.

FIG. 29 depicts a conceptual wiring diagram for a transfill switch 2901for completing a compressor 2904 power circuit supplied by source 2902and/or a solenoid 2905 power circuit supplied by source 2903, accordingto various embodiments of the present invention. Compressor 2904 isnormally off during liquefaction. Solenoid valve 656 is normally open,but may be closed during transfill in order to permit a pressure buildupinside dewar 620. Transfill switch 2901 may be depressed, for example,with the bottom of a portable stroller or portable dewar as it isengaged with a transfill valve; transfill switch may then complete thecompressor 2904 circuit and/or the solenoid 2905 circuit.

FIG. 30 depicts a transfill time-out flow chart, according to variousembodiments of the present invention. In one embodiment mentioned above,the transfill of liquid oxygen to a portable stroller may be activatedthrough a state change on the input of a programmable logic device,which may operate to activate the compressor 646, close the solenoidvalve 656, monitor the time since transfill began, and terminate thetransfill after a predetermined time. Various devices may be used toimplement elements of the flow diagram of FIG. 30; for example, suchdevices include, but are not limited to, a microcontroller and/orprocessor, discrete hardware semiconductors, and/or programmable logicdevices. According to some embodiments of the present invention, amethod may be used to stop the transfill process after a predeterminedtime to prevent over-filling of a portable stroller or portable dewar. Atransfill timing process begins at block 3001. A determination is madewhether the transfill switch is enabled (block 3002). If the transfillswitch is not enabled, the process continues just before block 3002. Ifthe transfill switch is enabled, then the compressor and solenoid areenabled (block 3003), as described with reference to FIG. 29, above. Atimer count is started (block 3004), using a clock in some embodiments.A determination is made whether the timer count equals a predeterminedcount (block 3005); for example, a determination is made whether thetimer count equals two minutes. As another example, the predeterminedcount may equal one minute and forty seconds. The predetermined count orpredetermined time may be any time based on the expected volume ofcontainer to be filled and/or the flow rate of liquid gas into thecontainer. Any such predetermined time may also take into account thefact that during the beginning of a transfill process, no liquid gas istransferred between the dewar and the portable stroller because theliquid gas initially boils off in making the transfill apparatus coldenough to convey the liquid gas. If the timer count does not equal thepredetermined count, then the timer count is positively incremented andthe process returns to a point just before block 3005. If the timercount equals the predetermined count, then the transfill time processends (block 3006).

FIG. 13 illustrates a portable stroller 1368 interface according to someembodiments of the present invention. In one embodiment, the transfillprocess begins when female valve 1377 on stroller 1368 is aligned withthe transfill valve 1364 and pushed onto the transfill valve 1364 in thedirection indicated by arrow 1367; a transfill switch 1366 may beconfigured to activate when a female valve 1377 on the stroller 1368 isengaged with the transfill valve 1364. According to some embodiments ofthe present invention, transfill switch 1366 is a push-button switchthat may be pushed or pressed by a valve interface surface 1397 ofportable stroller 1368 when female valve 1377 of portable stroller 1368has been engaged with valve 1364.

FIG. 24 illustrates a partial cross-sectional view of a male transfillvalve 2466 and female valve 2467 interface, according to someembodiments of the present invention. A gas liquefaction device may havemounted therein a valve mount 2473 in fluid communication with atransfill tube, such as a tube extending between valve mount 2473 and adewar operable to contain a liquid gas. According to some embodiments ofthe present invention, valve mount 2473 may have a threaded innerdiameter onto which a valve body 2475 having a threaded outer diametermay be attached. Valve body 2475 may include a fluid passage 2465through which fluids such as liquid oxygen may flow. A valve stem 2481may be situated within fluid passage 2465 and configured to close fluidpassage 2465 until depressed. One or more springs (not shown) may beused to bias valve stem 2481 in a closed position. Female valve 2467 mayinclude a valve body 2479 having a threaded outer diameter, for example,in order to be attached to a portable stroller. Female valve 2467 mayalso include a fluid passage 2463 and a valve stem 2477, the valve stem2477 being situated within fluid passage 2463 and configured to closefluid passage 2463 until depressed. Valve stem 2477 may also be biasedin a closed position via one or more springs (not shown). When aportable stroller comprising female valve 2467 is interfaced with aportable use liquefaction device having a transfill valve 2466, femalevalve 2467 may be pressed onto transfill valve 2466 to press valve stem2481 into valve stem 2477, thereby opening fluid passage 2465 and fluidpassage 2463 as shown in FIG. 24 to allow liquid gas, such as liquidoxygen, to flow from a dewar into a portable stroller. According to someembodiments of the present invention, a Teflon ring 2461 may be usedbetween female valve 2467 and transfill valve 2466 to temporarily sealthe valve interface while valve 2467 is pressed onto valve 2466, toprevent leakage of liquid gas during a transfill process.

As an additional safety measure, transfill valve 2466 and/or femalevalve 2467 may be specially adapted to be incompatible with traditionalUSP transfill valves. USP transfill valves may be used to transfer USP99% purity liquid oxygen from a dewar to a portable stroller; however,government regulatory entities may require that USP93 approved strollersbe incompatible with USP transfill valves. One embodiment of a solutionto such a problem is made possible by the existence of a de factostandard valve interface for USP portable strollers. Such a possiblesolution involves creating a valve mount 2473 having an outer diameter2471 greater than an inner diameter of a standard USP valve interface,such that the standard USP valve interface of a USP portable strollerdoes not fit over the valve mount 2473 and cannot depress valve stem2481 of a USP93 oxygen liquefaction device. A USP93 stroller may beconfigured with a female valve 2467 adapted with a larger inner diameter2469 to fit over valve mount 2473 and/or valve body 2475. Anotherembodiment of a solution for making transfill valve 2466 incompatiblewith a USP portable stroller may involve making the protruding maleportion of valve 2466, such as valve body 2475, shorter than a femalecavity of a USP portable stroller valve, such that pushing a USPportable stroller valve onto transfill valve 2466 would not bring thevalve stem of the USP portable stroller close enough to valve stem 2481to open either fluid passage 2463 or fluid passage 2465. According tosome embodiments of the present invention, although a portable strollerwith a standard USP valve would not fit over transfill valve 2466, aportable stroller with female valve 2467 could be configured to fit overtransfill valve 2466 and/or a standard USP transfill valve. Based on thedisclosure provided herein, one of ordinary skill in the art willrecognize a variety of ways in which transfill valve 2466 and/or femalevalve 2467 may be configured and/or modified to be incompatible with acorresponding USP (99% purity) approved valve.

With reference to FIG. 1, cryocooler 102 and dewar 120 interface atcryocooler flange 104 and dewar flange 116. An O-ring 106 may be placedbetween dewar flange 116 and cryocooler flange 104 to create a sealbetween dewar flange 116 and cryocooler flange 104. The O-ring 106 maybe made with silicon. A cold finger 108 having a cold head 110 extendsfrom cryocooler 102 down into the dewar 120. A feed flow of concentratedoxygen gas enters a feed tube 112 and is liquefied at the cold head 110,then falls into dewar 120. Boiloff gases from dewar 120 exit throughvent tube 114. A liquid oxygen barrier 118 may be situated between dewar120 and cryocooler 102 in order to control the flow of gas and expandingliquid when the dewar 120 is tipped onto its side.

Some prior gas liquefaction devices have typically employed complexand/or expensive condenser structures attached to a cold head of acryocooler. It has previously been thought advantageous to force a feedgas stream across a cold surface enclosure in order to improveliquefaction efficiency. It has also previously been thoughtadvantageous to employ a cooled structure, such as a double-walledcondenser structure attached to a cold surface of the cryocooler, and todirect the feed gas through the condenser structure to increase surfacearea over which liquefaction occurs. However, embodiments of the presentinvention simply employ a cold finger 108 structure with a cold head110, at which oxygen gas liquefies. Instead of forcing a feed stream ofgas onto cold finger 108, or through a high-surface area condensingstructure, embodiments of the present invention permit oxygen gas to beintroduced in the vicinity of cold finger 108 through feed line 112. Dueto the very cold temperatures produced by cold finger 108, a lowpressure area is created at the surface of cold finger 108; this lowpressure area, or “cold pressure,” draws the feed stream of gas towardcold finger 108 for liquefaction. Utilizing this concept in embodimentsof the present invention reduces cost and complexity by eliminating acondenser structure, particularly a complex or double-walled or spiraledcondenser structure.

Although flow director portion 2065 of liquid oxygen barrier 2061 maysurround cold head 110 of cold finger 108, or may stop short of coldhead 110, as described below with reference to FIGS. 20 and 21, flowdirector portion 2065 merely directs the flow of gaseous oxygen andother gases, and is not a condenser, according to various embodiments ofthe present invention. Flow director portion 2065 may direct incominggas through an inside of flow director portion 2065, causing it toremain in the vicinity of cold finger 108 and/or cold head 110. Outgoinggas, or vent gas, such as vent gas from dewar 120, may pass along anoutside of flow director portion 2065 as it exits through vent line 114.A smaller opening between cold head 2110 and flow director portion 2065may permit liquid oxygen to drip out after liquefaction, while a largeropening on the outside of flow director portion 2065 may permit gases,such as vent gases, to exit the dewar. Thus, flow director portion 2065serves to direct gas flow according to some embodiments of the presentinvention. According to some embodiments of the present invention, flowdirector portion 2065 may also serve to prevent liquefaction of ambientair directly following a transfill process.

For many of the same reasons that embodiments of liquefaction systemsdepicted in FIG. 1 do not require complex and/or expensive condenserstructures, so, too, embodiments of liquefaction devices depicted inFIG. 1 may also reduce liquefaction cost by seeking to maintain theoxygen purity of incoming gas, rather than seeking to maximize oxygenpurity of incoming gas. Embodiments of the present invention depicted inFIG. 1 may produce liquid oxygen with an oxygen purity approximately ator just above the oxygen purity of the incoming feed stream supply ofoxygen gas. This may be achieved, for example, by fixing the flow rateof the feed stream of oxygen from concentrator 530, using regulator 540and orifice 542, and by maintaining the cold finger 108 at asubstantially constant temperature at or below the liquefactiontemperature of oxygen. Many oxygen concentrators output oxygen gas witha USP93 purity. Embodiments of the present invention therefore liquefy afeed flow of USP93 oxygen gas to maintain purity by creating liquidoxygen with a USP93 purity, rather than liquefying a feed stream ofUSP93 gas to maximize liquefaction purity. Such maximization oftenrequires more complex controllers and hardware, often greatly increasesthe cost of oxygen liquefaction for small-scale home or office use, andtherefore stands as a common drawback associated with prior art devices.The efficient and effective maintenance of oxygen purity achieved byvarious embodiments of the present invention is made possible at leastin part by the particular designs, structures, operations, andplacements of cryocooler 102, dewar 120, feed line 112, vent line 114,cold finger 108, and other liquefaction-related structures ofembodiments of the present invention.

Once a liquefaction system according to embodiments of the presentinvention achieves equilibrium, there is a constant load on thecryocooler 102 due to the constant flow of gas to be liquefied, andconstant thermal losses of the system. Because power to the cryocooler102 also remains constant, the cold finger 108 may remain at asubstantially constant temperature until the dewar 120 is full. If allof the feed stream of gas were liquefied, oxygen purity of the liquefiedgas would remain the same as the oxygen purity of the feed stream ofgas. However, such systems may maintain or slightly improve oxygenpurity of the liquefied gas compared to the purity of the feed flow ofgas for the following reasons: the three primary components of air havethe following boiling points (liquefaction temperature): oxygen 90.2° K,argon 87.3° K, and nitrogen 77.4° K. Even at a cold finger 108 tiptemperature colder than 77° K, if a positive feed flow is maintained,not all of the feed stream of gas will be liquefied and a slightlygreater relative percentage of oxygen will liquefy versus argon andnitrogen. If the equilibrium temperature of such liquefaction systems is87° K, then only oxygen and argon would liquefy. A similar phenomenonmay also occur after liquefaction with preferential boiloff due to thedifferent boiling point temperatures of these three gasses. Becauseoxygen has a higher boiling point temperature than argon or nitrogen, aslightly lower percentage of oxygen boils off due to dewar 120 thermalinefficiencies. Even though preferential boiloff continues to occurafter the liquid gas is transferred from the storage dewar 120 in theliquefaction device to the portable dewar from which a patient maybreathe, the product gas will still maintain a purity at or greater thanthe initial feed gas prior to liquefaction. This is due to thepreferential liquefaction, and the preferential boiloff during storageand transfer that has already taken place increasing the liquid purityprior to a patient's breathing of the gas from the liquid portablestroller.

When a liquefaction device with an insulated dewar 120 tips over ontoits side with a dewar 120 full of liquid oxygen, the liquid oxygen canflow out of the mouth of the dewar 120 into the cryocooler flange 104.This area may be very warm with a large mass of metal, and may providedirect access to the feed tube 112 and vent tube 114. The sudden warmingof the liquid oxygen may cause the liquid to quickly boil resulting in arapid volumetric expansion. This rapid expansion may force liquid oxygenalong with gaseous oxygen through the feed tube 112 and vent tube 114and may result in a spray of liquid oxygen out of a vent port of theliquefaction device.

A liquid oxygen barrier 118 may be configured to significantly slow downthe rate at which liquid oxygen escapes from the insulated dewar 120during a tipping event. The liquid oxygen barrier 118 reduces the sizeof the opening out of which liquid oxygen may escape during tipping. Theliquid oxygen barrier 118 may have a diameter smaller than a diameter ofthe cryocooler flange 104, or the dewar flange 116, or both. The liquidoxygen barrier 118 may be a separate piece inserted between thecryocooler flange 104 and the dewar flange 116, or may be inserted intothe cryocooler flange 104 only, or may be inserted into the dewar flange116 only. Alternatively, the liquid oxygen barrier 118 may be integratedinto either the cryocooler flange 104 or the dewar flange 116.

FIG. 3 depicts a liquid oxygen barrier 318 inserted between cryocoolerflange 304 and dewar flange 316. O-ring 306 helps to create a sealbetween cryocooler flange 304 and dewar flange 316. Concentrated gasenters feed tube 312 prior to liquefaction; boiloff gas from dewar 320leaves through vent tube 314. Although the liquid oxygen barrier 318 mayallow a building pressure to vent upon tipping of the dewar 320, thepressure is allowed to vent at a controlled and safe rate. In oneembodiment, the liquid oxygen barrier 318 restricts an opening, aroundcold finger 308, between the dewar 320 and the cryocooler 302 to asmaller opening 301 of which the difference between an inner diameterand an outer diameter of the smaller opening 301 is approximately ten tofifteen thousandths of an inch. Smaller opening 301 may be locatedwithin an annular channel 395, the annular channel formed or defined bythe cryocooler flange 304 and/or dewar flange 316 on an outer side, andby the cold finger 308 and/or cryocooler 302 on an inner side, asdepicted in FIG. 3. Alternatively, annular channel 395 may be formed ordefined by the cryocooler 302 and/or dewar 320 on an outer side, and bythe cold finger 308 and/or cryocooler 302 on an inner side, as depictedin FIG. 3. Barrier 318 may serve to narrow the width of annular channel395, and/or reduce the cross-sectional area of annular channel 395, suchas at smaller opening 301. With barrier 318 in place, gas is stillpermitted to flow between the cryocooler 302 and the dewar 320; however,when the dewar 320 is tipped or tilted, barrier 318 may serve todecrease the rate at which a rapidly-expanding mixture of gas and liquidgas is permitted to exit the dewar 320 into the cryocooler 302. In apreferred embodiment, the liquid oxygen barrier 318 may be constructedwith Teflon.

According to some embodiments of the present invention, barrier 318 maybe positioned, inserted, or interposed between cryocooler flange 304 anddewar flange 316; in such embodiments, clamping element 1831, 1931 (seeFIG. 18, for example) may secure barrier 318 in place whilesimultaneously clamping cryocooler flange 304 and dewar flange 316together over O-ring 306. In other embodiments, barrier 318 may beintegral with cryocooler 302, dewar 320, and/or cold finger 308. FIG. 19also depicts a side perspective, cut-away view of an inside of acryocooler and dewar interface of one embodiment of the presentinvention, showing one embodiment of a cold finger and a liquid oxygenbarrier 1918.

Referring to FIGS. 20 and 21, an alternative embodiment of a liquidoxygen barrier 2061 is shown. Liquid oxygen barrier 2061, 2161 comprisesa liquid oxygen barrier portion 2063 and a flow director portion 2065.Flow director portion 2065 extends the length of a cold finger 2108.Flow director portion 2065 may alternatively extend the length of a coldfinger 2108 including a cold head 2110. Flow director portion 2065 maybe tubular; alternatively, flow director portion 2065 may be of anyshape that surrounds the cold finger 2108 and directs a feed gas flowfrom the feed line 512 towards the cold head 2110. In some embodiments,liquid oxygen barrier 2061, 2161 may be constructed with a Teflonmaterial. Feed flow enters from a feed flow line 512 through opening2069 and flows inside of the flow director portion 2065 toward the coldhead 2110. Vent gas flows along the outside of the flow director portion2065 and out to the vent line 514 through opening 2067. The liquidoxygen barrier portion 2063, though of a different configuration inorder to allow feed gas to flow inside and vent gas to flow outside,performs the same function as the liquid oxygen barriers 118, 318, 1918in preventing excessive leakage of liquid and gaseous oxygen during atipping event.

FIGS. 9-11 depict perspective views of a lower chassis assembly of aliquefaction device according to one embodiment of the presentinvention. Shown in FIGS. 9-11 are feed tube 912, 1012; vent tube 914,1014; solenoid valve 1056; relief valve 1054 for the feed tube 1012;filter 1052; relief valve 1158 for the vent tube 1014; vent port 1170;and boiloff tube 1160. In one embodiment, feed tube 1012 and/or venttube 1014 are one quarter inch inner diameter vinyl tubing. Also shownare mounting slots 1172 onto which an upper chassis assembly may beinserted.

FIGS. 12 and 13 depict a perspective view of the outer housing 1280 of aliquefaction apparatus according to one embodiment of the presentinvention, showing a possible placement of a detachable humidifier 1284.Humidifier bottle 1284 is attached to patient flow tube 534. Ahumidifier may not be used at the outlet of the oxygen concentrator 530because the liquefaction process cannot tolerate water vapor mixed withoxygen. In one embodiment, humidifier bottle features an attachmentnozzle 1286 for attaching a canula. Patient flow meter 1238 allows apatient to adjust flow rate of oxygen received. The top of the outerhousing 1280 features an indentation 1282 in the shape of the bottom ofa portable stroller 668 to facilitate fitting the stroller 668 overtransfill valve 1264. The indentation 1282 also accommodates theportable stroller 668 in order to allow the portable stroller 668 todepress a transfill switch 666. Indentation 1282 may be a depressionformed on outer housing 1280, shaped to fit a valve interface surface697 of portable stroller 668. The stroller 668 also has a valve thatinterfaces specifically with transfill valve 1264, such that when thestroller 668 is engaged onto the transfill valve 1264, a connectionopens between the two valves allowing fluid to flow freely between them.

In one embodiment, outer housing 1280 has handles 1288. Handles 1288 mayfacilitate patient handling and movement of the liquefaction device.Handles 1288 may also be configured to allow a canula to be wrappedaround them for storage while the canula is not in use. Alternatively,handles may be secured into the outer housing 1280 with fasteners thatare also operable to hold wires in the correct place along the inside ofthe outer housing 1280. For example, if the handles 1288 are secured tothe outer housing 1280 with screws, a wire on the inside of the outerhousing 1288 may be laid under a strap secured to the inside of theouter housing 1288 between two screw heads, thus securing a placement ofthe wire. In one embodiment, the handles may be integral to the outerhousing 1288.

FIG. 14 depicts a top perspective view of the outer housing 1480 of aliquefaction device according to one embodiment of the presentinvention, showing one embodiment of a transfill valve 1464 andtransfill switch 1466.

FIG. 15 depicts a side perspective view of a cryocooler 1502 and dewar1520 secured by a mounting shroud 1590 to an upper chassis 1594 of aliquefaction device according to one embodiment of the presentinvention. The mounting shroud 1590 comprises a cooling fan mount 1592.In one embodiment, the upper chassis 1594 has mounting pegs 1596 thatfit into mounting slots 1172 (see FIG. 11) on a lower chassis. In oneembodiment, mounting shroud 1590 is secured to upper chassis 1594 viavibration dampeners 1598. The vibration dampeners 1598 greatly reducenoise due to vibration by isolating the cryocooler 1502 and mountingshroud 1590 from the upper chassis 1594 at the places where the mountingshroud 1590 contacts the upper chassis 1594: the four mounting bolts.Vibration dampeners 1598 may be made with rubber. For example, vibrationdampeners 1598 may be made with Buna-N rubber. Alternatively, vibrationdampeners 1598 may be made with any other vibration-dampening materialsor devices. For example, vibration dampeners 1598 may comprise a springdampener assembly.

FIG. 16 depicts a perspective view of a back side of the mounting shroud1690 and dewar 1620 according to one embodiment of the presentinvention. The shape of the inside of the mounting shroud 1690 may besuch that it directs airflow over a cooling fin of a cryocooler. A fanmay be mounted in fan housing 1692 to pull air in the directionindicated by arrow 1675. Consequently, air enters the air intake 1671 inthe direction indicated by arrow 1673, blows over a cooling fin of thecryocooler, and exits the mounting shroud 1690 through fan housing 1692.FIG. 17 shows a partial cutaway view of the mounting shroud 1790,revealing cryocooler 1702 and cryocooler cooling fin 1711.

FIG. 18 depicts an interface between a cryocooler flange 1804 and adewar flange 1816 according to one embodiment of the present invention.The mounting shroud 1890 may comprise two separate pieces. The mountingshroud 1890 may alternatively comprise two halves. Two mounting shroudhalves may be bolted together through bolt holes such as bolt hole 1677.In one embodiment, mounting shroud 1890 comprises a clamp, or clampingelement, 1831, 1931. Clamping element 1831, 1931 encompasses at least aportion of both cryocooler flange 1804 and dewar flange 1816, as shownin FIG. 18. The cryocooler flange 1804 may include a sloped portionsurface leading out from a neck portion 1835 of the cryocooler, as theouter diameter of cryocooler flange 1804 increases as it approachesdewar flange 1816. Dewar flange 1816 may also include a correspondingsloped portion surface leading out from a neck portion 1833 of thedewar, as the outer diameter of dewar flange 1816 increases as itapproaches cryocooler flange 1804. Clamp 1831, 1931 may be configured toconform to the sloped portion surfaces of dewar flange 1816 andcryocooler flange 1804, in order to, for example, apply a normal forcethereto. A normal force applied to the sloped portion surfaces of thecryocooler flange 1804 and the dewar flange 1816, as two halves of theclamping element 1831, 1931 are secured around the flanges 1804, 1816and tightened, creates a corresponding axial force that pushes the twoflanges 1804, 1816 together. The compression of the O-ring 106 thatfollows application of the clamping element 1831, 1931 serves to preventthe cryocooler flange 1804 and dewar flange 1816 interface from leakingeither gaseous or liquid oxygen, even when tipped over.

With reference to FIG. 4, a mechanical, rather than electrical, meansfor stalling liquid oxygen production is shown according to oneembodiment of the present invention. A cold finger 408 extends intodewar 420. Cold finger 408 has a temperature gradient. One end 413 ofcold finger 408 has a temperature higher than the boiling point ofoxygen, and another end 415 has a temperature lower than the boilingpoint of oxygen. As oxygen liquefies and fills the dewar 420, the liquidlevel 417 rises only to a level on the cold finger 408 at which thetemperature exceeds the boiling point of oxygen. At this level 417, noexposed part of the cold finger 408 is cold enough to liquefy oxygen, sothe liquid level 417 does not rise further; this prevents overfilling ofthe dewar 420.

Alternatively, a cryogenic liquid level sensor 789 may be used totrigger a system shutdown when the liquid level in the dewar exceeds apredetermined limit. FIG. 7 depicts a side view of a cryogenic liquidlevel sensor 789 of one embodiment of the present invention. Parallelplates 783 may be held together with non-conductive screws 781 on eitherside of a mounting plate 785; cryogenic liquid level sensor 789 may becoupled to top of dewar 820 and extend the length of the dewar 820, asaccording to one embodiment of the present invention depicted in FIG. 8.A capacitive method of measuring the level of liquid gas, such as liquidoxygen, in a dewar may be utilized. This method may use parallel plates783 or parallel cylinders (not shown). As the liquid level in the dewar820 rises, the gaseous oxygen between parallel plates 783 is graduallyreplaced with liquid oxygen. The dielectric-constant change betweengaseous oxygen and liquid oxygen varies the capacitance measured betweenparallel plates 783. This capacitance change corresponds to the liquidlevel change in the dewar 820, and may be measured and converted to ausable form for display to a user. In one embodiment, the liquid levelin the dewar is displayed in a bar-lamp format with a resolution of ¼dewar (¼, ½, ¾, full). In one embodiment, liquid level in the dewar 820is displayed in a digital readout.

A capacitor cryogenic liquid level sensor 789 may be constructed of twoor more metal electrically conductive plates separated by anon-conductive material having a fixed dielectric constant, such as adielectric constant greater than 1.0. Such a cryogenic liquid levelsensor 789 may be used to measure the liquid level of liquid oxygen ornearly any other cryogenic liquid. Cryogenic oxygen liquid level sensor789 may measure the difference of the change in the dielectric constantof oxygen between the gaseous phase and the liquid phase. This creates avariable capacitance directly related to liquid height. A number ofdifferent displays of liquid level may be possible with the use ofcryogenic liquid level sensor 789.

Other types of cryogenic liquid level sensors may be used, according toalternative embodiments of the present invention. For example, a floatmay be used to measure cryogenic liquid level in a manner similar to themanner in which a float may be used as a common automotive fuel levelsensor. In such cases, a float arm moves through a variable resistanceas the float moves up or down on the surface of the desired liquid. Thisvariable resistance produces a variable voltage from a known voltagesource, and the variable voltage may be connected to a voltage meter orthe like for display. According to other alternative embodiments ofcryogenic liquid level sensors, a resistance method may be used. Suchmethods may, for example, utilize the thermal conductivity constant forcopper (3.98 watts per centimeter—Kelvin), and the resistivity constantof copper, to sense the point between the gaseous phase and the liquidphase of the cryogenic liquid. Such a level point between the gaseousphase and the liquid phase has a differential temperature change, suchas a differential temperature change of a few degrees, and thus adifference in the thermal conductivity because the gaseous phaseconducts more power than the liquid phase. The liquid height may becalculated based on the level of the liquid phase as sensed by theamount of power conducted to the gaseous phase; a lower power conductedto the gaseous phase may correspond to a higher liquid level. Accordingto yet other alternative embodiments of cryogenic liquid level sensors,semi-conductor methods may be used. Such methods may employ a specialdiode construction whose conduction properties change when exposed tocryogenic temperatures; in some instances, the special diodeconstruction may be an individual point(s) monitoring device controlledvia a microcontroller/processor. According to further alternativeembodiments of cryogenic liquid level sensors, ultra-sonic methods maybe used. Such methods may use a pulsed high or ultra-high frequencyultrasonic transducer to measure the “Doppler Effect” of the reflectedsignal from the surface of the measured liquid. A shorter “DopplerEffect” measurement corresponds to a higher cryogenic liquid level.

FIG. 22 depicts an efficient dewar 2220 design. Liquid oxygen may bestored in an inner vessel 2217. The inner vessel 2217 is contained bythe outer vessel 2215. Between the inner vessel 2217 and outer vessel2215 is a near-vacuum space to minimize convective heat transfer. Awrapping material 2219, such as SuperWrap, is wrapped around the innervessel 2217 to slow radiant heat transfer. Cold getters 2211 captureerrant moisture molecules from within the vacuum space. A warm surfacegetter 2213 captures hydrogen molecules from within the vacuum space. Atransfill tube 2262 reaches through the inner vessel 2217, then wrapsseveral times around the bellows neck 2221, then exits through the outervessel 2215. By increasing the length of the transfill tube 2262 withinthe vacuum space, and by narrowing the cross-sectional area of the tube2262, conductive heat losses are minimized. Conductive heat losses arealso minimized by the bellows neck 2221. The inner vessel 2217 iscoupled to the outer vessel 2215 by bellows neck 2221. Bellows neck 2221may have an accordion shape, as depicted in FIG. 22, in order toincrease the length of the path that heat must travel to escape. Otherbellows neck 2221 designs may be employed to increase the length of thepath that heat must travel to escape.

Referring now to FIG. 2, a fin temperature sensor 299 may be located inproximity to a cooling fin of a cryocooler. Additionally, a cold fingertemperature sensor 297 may be located in proximity to a cold finger of acryocooler. The fin temperature sensor 299 may detect potentiallyhazardous or damaging conditions; for instance, sensing a fintemperature that is too high may indicate that the cooling fan hasfailed and the cryocooler is overheating. The fin temperature sensor 299may also detect whether the liquefaction apparatus has been placed insunlight, an excessively warm room, or whether its cooling vents havebeen obstructed. Cold finger temperature sensor 297 may detect if adisplacer in the cryocooler has seized, causing the cold finger to warmup rather than cool down. In embodiments that use alternative liquidoxygen barrier 2061 (see FIGS. 20-21), cold finger temperature sensor297 may alternatively be located inside of flow director portion 2065.When either fin temperature sensor 299 or cold finger temperature sensor297 senses a temperature that is too high, a circuit latches a “halt”signal to the cryocooler control and stops the motor. An indicator lampfor the user may be illuminated during this fault. The “halt” signal maybe released by recycling power to the liquefaction apparatus, unless theexcessive temperature condition is still present.

FIG. 27 depicts a conceptual wiring diagram for a temperature sensingcircuit to turn off electrical components of a liquefaction system,according to various embodiments of the present invention. A signalconditioner may be coupled with temperature sensors or thermocouples2701, 2702. The signal conditioner outputs a temperature signalcorresponding to one, both, or more of temperature sensors 2701, 2702.As one example, temperature sensor 2701 may be located and/or configuredto measure the temperature near a cooling fin of a cryocooler 2704, alsoknown as the reject temperature. As yet another example, temperaturesensor 2702 may be located and/or configured to measure the temperaturenear a cold finger of a cryocooler 2704. The signal is compared to areference voltage by a comparator 2707. When either temperature sensor2701, 2702 senses a temperature that is too high, the depicted circuitlatches a “halt” signal to the cryocooler PWM control 2706 and stops themotor of cryocooler 2704 by breaking the electrical power circuitsupplying power from source 2705 to cryocooler 2704. Power may beremoved from cryocooler 2704 when either temperature sensor 2701 ortemperature sensor 2702 senses a temperature that is too high; forexample, according to some embodiments of the present invention,temperature sensor 2701 may sense a cryocooler cooling fin temperatureabove sixty-five degrees Celsius, or temperature sensor 2702 may sense acold finger temperature above fifty degrees Celsius. An indicator lampfor the user may be illuminated during this fault. The “halt” signal maybe released by recycling power to the liquefaction apparatus, unless theexcessive temperature condition is still present.

FIG. 25 depicts a conceptual wiring diagram for an impact-sensingmechanism to turn off electrical components of a liquefaction system,according to various embodiments of the present invention. Powersupplied by source 2506 to a load 2505 is passed through an actuatedcontact assembly (i.e. circuit breaker or relay or semi-conductorcircuit). As long as power is applied to the actuator mechanism 2504,power is allowed through the contact assembly. During a tip-overcondition, the sensing output of an accelerometer 2501 or other impactsensing device 2501 is amplified into a desired range by amplifier 2502.This voltage range is input into an analog-to-bit converter and comparedto a known voltage at comparator 2503. The “bit” output triggers aswitching device. When the switching device is active, a circuitprotector device removes the power to the actuator mechanism 2504 andremoves power to the load 2505. Load 2505 may be, but is not limited to,the cryocooler, cryocooler driver, cooling fan, circuit boards, and/orany other element that operates via electrical power.

FIG. 26 depicts a conceptual wiring diagram for a tip-over or tiltswitch to turn off electrical components of a liquefaction system,according to various embodiments of the present invention. Tip/tiltswitch 2601 may be any switch capable of changing states, from “on” to“off” or from “off” to “on,” when tip/tilt switch 2601 experiences arotation in angle or inclination. Tip/tilt switch 2601 may be affixed toa dewar, cryocooler, and/or any other element of a gas liquefactionsystem to determine when the element to which it is attached has beentipped and/or tilted. For example, tip/tilt switch 2601 may be a mercuryswitch. Tip/tilt switch 2601 may be configured to change states upontipping or tilting through a predetermined angle; for example, thepredetermined angle may be forty-five degrees. Alternatively, thepredetermined angle may be any angle indicative of a tipover orexcessive tilting event; for example, the predetermined angle may be anangle in the range from thirty degrees to sixty degrees. Power from asource 2606 to a load 2605 is passed through an actuated contactassembly (i.e. circuit breaker or relay or semi-conductor circuit). Aslong as power is applied to the actuator mechanism 2604, power isallowed through the contact assembly. During a tip-over condition,tip/tilt switch 2601 triggers to remove power to the actuator mechanism2604, thereby removing power to the load 2605. Load 2505 may be, but isnot limited to, the cryocooler, cryocooler driver, cooling fan, circuitboards, and/or any other element that operates via electrical power.

FIG. 28 depicts a conceptual wiring diagram for measurement of oxygenpurity and display options for displaying oxygen purity, according tovarious embodiments of the present invention. Several methods of oxygenpurity sensing exist; for example, oxygen purity may be measured with aGalvanic-type micro-“fuel-cell” method, or with a light refractionmethod. Each oxygen purity sensing element may provide a differentusable output, and each may require its own conversion circuitry.Similarly, each possible method for displaying oxygen purity informationmay requires its own conversion circuitry and/or method. As illustratedin FIG. 6, oxygen purity sensor 568 may be located in feed flow line512. For example, oxygen purity sensor 568 may be located in fluidcommunication with feed flow line 512 and/or inline with feed flow line512 anywhere prior to liquefaction. If oxygen purity sensor 568 issensitive to input pressure, oxygen purity sensor may be placed in feedflow line 512 downstream from pressure regulator 540 and/or orifice 542.

According to one embodiment of the present invention, a sensor 2801,such as a “fuel-cell” sensor, may be used to measure oxygen purity. Asensed oxygen purity may be displayed through various graphicalrepresentations, such as, for example, numerical LED indicators 2803,purity bar LED indicators 2804, and/or colored LEDs 2805. The usablesensing output of the “fuel-cell” may be, but is not limited to, asignal corresponding to millivolts per percent of oxygen. This signalmay be amplified into a required voltage range. When using a simplepass/fail type of information display, the amplified signal may be inputto a series of analog-to-bit converters. A display driver 2802 may thenswitch ON independent LED's or lamps to indicate a pass/fail conditionof the gaseous oxygen purity level. For example, display driver 2802 maydisplay a numerical purity measurement via numerical LED indicators2803. According to some embodiments, display driver 2802 may display agraphical purity measurement via a purity bar LED indicator 2804.According to yet other embodiments, display driver 2802 may display apass/fail purity measurement via green, yellow, and/or red LEDs 2805; insuch cases, activation of a green LED may signal a satisfactory oxygenpurity level, activation of a yellow LED may signal a potential thoughnot necessarily serious problem with oxygen purity, and activation of ared LED may signal a serious or dangerously low oxygen purity level.According to some embodiments of the present invention, the satisfactoryoxygen purity range a purity greater than 85% oxygen by volume.

FIG. 31 depicts a conceptual wiring diagram illustrating a cryocoolerlow power mode, according to various embodiments of the presentinvention. When the dewar is full in a liquefaction apparatus ofembodiments of the present invention, the cryocooler continues to run,but does not continue to liquefy oxygen. This is due to the liquid levelrising to a point on the cold finger such that no exposed portion of thecryocooler's cold finger is colder than the liquefaction temperature ofoxygen. Continuing to run the cryocooler at full power with a full dewarmay result in an over-expenditure of energy. Although electrical powermay be removed completely from the cryocooler when a full dewar issensed, lowering power instead of removing power may reduce wear oncryocooler components and eliminate any potential noise associated witha cryocooler cold start. Potential advantages of implementing a lowpower mode of the cryocooler and/or cooling fan include, but are notlimited to, a reduced noise level, a reduction in excess heatgeneration, reducing liquid boiloff rate for liquid gas within thedewar, and/or decreasing cryocooler wear. Implementing a low power modeof the cryocooler and/or cooling fan may reduce power consumption byover fifty percent while the dewar is full, and may reduce powerconsumption by thirty to thirty-five percent overall. According to someembodiments of the present invention, a low power or energy saving modemay be initiated when the cryogenic liquid level sensor sensed a fullliquid level in the dewar, and may return to a normal mode when thecryogenic liquid level sensor sensed a predetermined liquid level in thedewar; for example, the low power mode may return to the normal modewhen the cryogenic liquid level sensor senses a three-fourths fullliquid level in the dewar.

According to some embodiments of the present invention, a low power modemay be entered by simply reducing the power supplied to the cryocoolerand/or cooling fan to a predetermined power level. FIG. 31 shows oneembodiment of a circuit operable to reduce power to the cryocoolerdriver 3102. In normal operation, the full PWM setpoint 3101 voltage maybe applied to the cryocooler driver 3102. The cryogenic liquid levelsensor supplies a liquid level voltage 3103 that may be amplified andcompared with a reference voltage to determine when the liquid level isfull and thus when the low power mode should be entered. When the lowpower operation is initiated, a switching device provides a ground paththrough an additional resistance, creating a voltage divider reducingthe voltage applied to the cooler driver 3102 circuitry. The appliedpower may be set to a wide range of possible powers, depending on theenergy consumption requirements of the cryocooler, and the fluid flowand/or thermodynamic characteristics of the given liquefaction system.According to some embodiments of the present invention, the appliedpower may be selected to keep the piston within the cryocooler centeredbut not displacing through its full range.

FIG. 32 depicts a conceptual wiring diagram illustrating an alternatingcurrent cooling fan low power mode, according to various embodiments ofthe present invention. A first circuit diagram 3201 illustrates a lowpower mode for an alternating current fan 3203 supplied with power bysource 3204. During normal operation, a full setpoint voltage is appliedto a PWM/Random phase controller 3205 having a timer 3206, and appliesfull voltage to the cooling fan 3203. When a lower fan speed is desiredto reduce noise and when full LOX production is not required, aswitching device may be activated creating a ground path through asecond resistance. Such a switching device may be activated when acryogenic liquid level sensor supplies a liquid level voltage 3207signal that exceeds a reference voltage. This creates a voltage dividercircuit and reduces the voltage setpoint for the PWM/random phase fandriver 3205 and slows the fan speed.

FIG. 33 depicts a conceptual wiring diagram illustrating a directcurrent cooling fan low power mode, according to various embodiments ofthe present invention. A second circuit diagram 3202 illustrates a lowpower mode for a direct current fan 3208. Rather than reducing powerwhen the production of liquid gas is no longer required, fan speed maybe automatically reduced or increased to maintain a constant cryocoolerreject temperature (or cooling fin temperature) at a predefinedtemperature. The reject temperature may be monitored and compared to asetpoint. Based on this difference, a switching device may be pulsed ata higher or lower rate by the PWM controller 3209, controlling the fan3208 air flow and set temperature of the cryocooler.

According to embodiments in which a low power mode is entered by simplyreducing the power supplied to the cryocooler to a predetermined power,the system eventually arrives at equilibrium, at which the temperatureof the cold finger tip may depend on a combination of factors,including, but not limited to the cooling efficiency of the cryocoolerand the thermal load to which the cryocooler is subjected. The thermalload experienced by the cryocooler may depend on factors including, butnot limited to, the flow rate of gas directed across the cold finger,the inlet temperature of the gas, and the thermal inefficiencies of thedewar and dewar seal flange. Because variations may exist in all ofthese parameters based on physical differences between separatelymanufactured components, an inlet power to the cryocooler should be sethigh enough to accommodate for the worst case variation. Such acryocooler power setting may result in the cryocooler drawing a powergreater than the power necessary to achieve an adequate liquefactionrate. Such extra power would generally further reduce the temperature ofthe cold finger during liquefaction. However, according to somealternative embodiments of the present invention, instead of simplyreducing power supplied to the cryocooler to a predetermined level, alow power mode may be entered by monitoring the temperature of the coldend of the cold finger and adjusting power input to the cryocooler tomaintain a predetermined cold end temperature during a low power mode.In such alternative embodiments, liquid may be produced until the dewaris filled, then the power supplied to the cryocooler may be reducedwhile monitoring the cold finger tip temperature. The predetermined coldend temperature may be found by experimentally varying the temperatureuntil a temperature is found that maintains the liquid volume within thedewar measured by a scale. Such a method may, in some cases, permit amore cost-effective and energy-saving design of a liquefaction system,and may also compensate for potential decrease in cryocooler efficiencyover time.

A liquefaction apparatus may also employ other electronic systems toimprove safety, efficiency, and cost. For instance, when power is firstapplied to the system, all the user indicator lamps may be activated toallow a user to verify that all lamps work properly; after a shortperiod of time, the lamps, except for the power lamp, may be deactivatedand the system may enter normal operation.

Additionally, various electronic means may be employed to control thecryocooler. The cryocooler firing angle may be varied so that the properRMS voltage is applied to the linear motor, maintaining the desiredpiston stroke, as external operating conditions change. A piston strokecontrol loop compares the stroke set-point to the piston amplitude froma re-construction circuit. This may be accomplished by controlling thefiring angle to a random-phase, opto-isolation Triac-driver. The firingTriac device and the front-end re-construction circuit may beelectrically isolated from the control and feed-back circuitry. Also,the stroke of the cryocooler piston may be estimated using an isolatedback-EMF of the motor and an isolated monitoring of the motor current.Integration of the resultant motor velocity results in a real-time,sensor-less measurement of piston stroke. At the start of the cryocoolerpower-up sequence, the cryocooler piston is lifted to its maximum stateby rectifying the AC voltage and controlling the resultant DC power tothe cooler. This is accomplished by controlling the firing angle to arandom-phase, opto-isolation Triac-driver and the use of a full-waveDiode-Bridge and a Triac combination.

FIG. 34 depicts a flow diagram 3400 illustrating a method formaintaining oxygen purity in liquefaction of gas for residential oxygentherapy, according to various embodiments of the present invention. Afeed stream of gas is received from an oxygen concentrator (block 3402).A cryocooler is provided, the cryocooler including a cold finger, andthe cold finger extending within a container and operable to liquefy thegas for containment in the container (block 3404). The cold finger maybe maintained at a substantially constant temperature at or below theliquefaction temperature of oxygen (block 3406). At least part of thefeed stream of gas is liquefied, the oxygen purity of liquefied gasbeing substantially at or greater than the oxygen purity of the feedstream of gas (block 3408). The feed stream of gas may be drawn to thecold finger at least in part with a low pressure created by liquefactionof the feed stream of gas at a surface of the cold finger (block 3410).Liquefied gas may be accumulated in the container (block 3412).According to some embodiments of the present invention, a portable dewarmay be provided to store the liquefied gas for ambulatory medical gastherapy (block 3414), and the liquefied gas may be transferred from thecontainer to the portable dewar (block 3416).

FIG. 35 depicts flow diagrams illustrating a method for reducing powerconsumption in residential medical gas liquefaction and storage and amethod for initiating a low power mode of a cryocooler, according tovarious embodiments of the present invention. Flow diagram 3500illustrates a method for reducing power consumption in residentialmedical gas liquefaction and storage. A feed stream of gas may bereceived from an oxygen concentrator (block 3502). A cryocooler may beprovided, the cryocooler including a cold finger, and the cold fingerextending within a container and operable to liquefy at least part ofthe feed stream of gas for containment in the container (block 3504). Aliquid level sensor may be mounted within the container, the liquidlevel sensor operable to detect a liquid level in the container (block3506). A determination is made whether the detected liquid level is ator greater than the first predetermined liquid level (block 3508). Ifnot, then the liquid level sensor continues to detect the liquid level(block 3508). If the detected liquid level is at or greater than thefirst predetermined liquid level, such as a full liquid level, then alow power mode of the cryocooler may be initiated (block 3510).

Flow diagram 3501 illustrates a method for initiating a low power modeof a cryocooler. A maintenance temperature may be selected (block 3512),and the temperature of the cold finger may be monitored (block 3514).The power supply to the cryocooler may be varied in order to maintainthe temperature of the cold finger at the maintenance temperature (block3516).

FIG. 36 depicts flow diagrams 3600, 3601 illustrating methods forinitiating a low power mode of a cryocooler, according to variousembodiments of the present invention. Flow diagram 3600 illustrates amethod for initiating the low power mode of the cryocooler. The powersupply of the cryocooler may be reduced to a low power setting (block3612). A determination may be made whether the liquid level in the dewaris at or below the second predetermined liquid level (block 3614). Ifnot, then the liquid level detection may continue (block 3614). If theliquid level in the dewar is at or below the second predetermined liquidlevel, such as at a three-fourths full level, then the power supply tothe cryocooler may be restored to a full power setting (block 3616).Flow diagram 3601 illustrates further elements of a method forinitiating a low power mode. A cooling fan may be provided (block 3618).The power supply of the cooling fan may be reduced to a low powersetting (block 3620). A determination may be made whether the liquidlevel in the dewar is at or below the second predetermined liquid level(block 3622). If not, then the liquid level detection may continue(block 3622). If the liquid level in the dewar is at or below the secondpredetermined liquid level, such as at a three-fourths full level, thenthe power supply to the cooling fan may be restored to a full powersetting (block 3624).

While the preferred embodiments of the invention have been illustratedand described, it will be clear that the invention is not limited tothese embodiments only. Numerous modifications, changes, variations,substitutions, and equivalents will be apparent to those skilled in theart, without departing from the spirit and scope of the invention, asdescribed in the claims. For example, use of the term “oxygen” in thisdisclosure may generally be substituted with any liquefiablemedically-useful gas, such as nitrogen, oxygen, argon, air, and/or amixture thereof. In addition, although reference is made tomedically-useful gas, embodiments of the present invention may be usedto produce liquid gas useful for industrial or other purposes.

1. A method for reducing power consumption in residential medical gasliquefaction and storage, the method comprising: receiving a feed streamof gas from an oxygen concentrator; liquefying at least part of the feedstream of gas via a cryocooler; containing the liquefied gas in acontainer; mounting a liquid level sensor within the container, theliquid level sensor operable to detect a liquid level in the container;initiating a low power operational mode of the cryocooler when theliquid level reaches a first predetermined liquid level by reducing apower supply of the cryocooler to a predetermined low power setting; andrestoring the power supply of the cryocooler to a predetermined fullpower setting when the liquid level has dropped below a secondpredetermined liquid level, wherein the second predetermined liquidlevel is different from the first predetermined liquid level.
 2. Themethod of claim 1, wherein the first predetermined liquid level is afull liquid level.
 3. The method of claim 1, wherein the secondpredetermined liquid level is a three-fourths frill liquid level.
 4. Themethod of claim 1, wherein initiating the low power operational mode ofthe cryocooler further comprises: providing a cooling fan operable toremove heat from the cryocooler; reducing a power supply of the coolingfan to another predetermined low power setting; and restoring the powersupply of the cooling fan to another predetermined full power settingwhen the liquid level has dropped to the second predetermined liquidlevel.
 5. The method of claim 1, wherein the cryocooler comprises a coldsurface, and wherein initiating the low power operational mode of thecryocooler comprises: selecting a maintenance temperature for the coldsurface needed to maintain the liquid level at full; monitoring atemperature of the cold surface; and varying a power supply of thecryocooler to maintain the temperature at the maintenance temperature.6. The method of claim 1, the method excluding: varying pressure withinthe container or flow rate of the feed stream of gas duringliquefaction.
 7. The method of claim 1, wherein the liquid level sensoris a capacitive-type liquid level sensor.
 8. A method for reducing powerconsumption in residential medical gas liquefaction and storage, themethod comprising: receiving a feed stream of gas from an oxygenconcentrator; providing a cryocooler comprising a condenser, thecondenser operable to liquefy at least part of the feed stream of gasfor containment in a container; mounting a liquid level sensor withinthe container, the liquid level sensor operable to detect a liquid levelin the container; initiating a low power operational mode of thecryocooler when the liquid level reaches a first predetermined liquidlevel by reducing a power supply of the cryocooler to a predeterminedlow power setting; and restoring the power supply of the cryocooler to apredetermined full power setting when the liquid level has dropped belowa second predetermined liquid level, wherein the second predeterminedliquid level is different from the first predetermined liquid level. 9.The method of claim 8, wherein the first predetermined liquid level is afull liquid level.
 10. The method of claim 8, wherein the secondpredetermined liquid level is a three-fourths frill liquid level. 11.The method of claim 8, wherein initiating the low power operational modeof the cryocooler further comprises: providing a cooling fan operable toremove heat from the cryocooler; reducing a power supply of the coolingfan to another predetermined low power setting; and restoring the powersupply of the cooling fan to another predetermined full power settingwhen the liquid level has dropped to the second predetermined liquidlevel.
 12. The method of claim 8, wherein initiating the low poweroperational mode of the cryocooler comprises: selecting a maintenancetemperature for the condenser needed to maintain the liquid level atfull; monitoring a temperature of the condenser; and varying a powersupply of the cryocooler to maintain the temperature at the maintenancetemperature.
 13. The method of claim 8, the method excluding: varyingpressure within the container or flow rate of the feed stream of gasduring liquefaction.
 14. The method of claim 8, wherein the liquid levelsensor is a capacitive-type liquid level sensor.